The present invention is directed to a gas-fueled rotary combustion engine in which a gaseous fuel charge is injected after the intake air port closes and early in the compression stroke for providing a fuel-charge stratification. This provides the advantages of increased thermal efficiency and volumetric efficiency, reduced exhaust emissions levels, and less tendency to detonate than a homogeneous charged engine.
In general rotary combustion engines have not been able to achieve brake thermal efficiencies as high as that of reciprocating engines. The two primary reasons for this lower efficiency are the rotary's large surface area-to-volume ratio of the combustion chamber and the long cycle time (1.5 times that of the reciprocating engine). Both these factors increase the amount of heat energy lost during combustion. The large surface area-to-volume ratio (a result of the long rectangular shaped chamber) also increases the time required to burn the mixture since the flame has farther to burn and increases the amount of unburned end gas in the combustion chamber. A lean fuel mixture is desirable because it facilitates high thermal efficiency, but at the same time it slows the burn rate which counteracts the benefits of lean burn efficiency.
Based on these rotary engine characteristics, a method is needed which will allow the engine to operate at lean overall fuel-air ratios (to attain high thermal efficiency) while maintaining, or even increasing, the burning rate of the fuel. Ideally a stratified fuel charge which is rich near the spark plugs and lean around the perimeter of the chamber is desired. This will keep the initial burning rate high due to a rich local mixture around the spark plugs and eliminate the unburned gas near the edges of the chamber.
The present invention is directed to achieving improved thermal efficiency and lowered exhaust emissions in a rotary combustion engine through fuel-charge stratification by injecting the gaseous fuel after the intake port closes for providing a stratified charge at combustion.